1. Field of the Invention
The present invention relates to a variable nozzle control apparatus of a turbocharger for controlling the opening of the vane of a variable nozzle of a turbocharger mounted on a car by means of an electronic control actuator in response to a control signal transmitted from an engine ECU.
2. Related Art
Conventionally, a technique for controlling the opening of the vane of a variable nozzle of a turbocharger mounted on a car of this type has a structure shown in FIG. 8, for example.
Description will be given to the structure. 1 denotes an engine ECU which is mainly constituted by a microcomputer including a CPU, an ROM, an RAM and an I/O circuit which are well known. The engine ECU 1 includes an electronic control throttle valve capable of variably regulating the amount of air taken into an internal combustion engine (engine) and serves to carry out an operation for opening and closing the electronic control throttle valve. The engine ECU 1 inputs the detection signals of a water temperature sensor, a rotation sensor and a load sensor which are provided in the engine (not shown), and detects an air-fuel ratio, an engine water temperature, an engine speed, an intake air amount and a fuel injection amount. 2 denotes a duty solenoid valve which is provided on the air intake tube side of the engine and serves to introduce air from the atmosphere. The duty solenoid valve 2 regulates an air pressure by an actuator, for example, a negative pressure actuator 3 so that an opening thereof is regulated and the amount of the air taken into the engine is regulated. Moreover, the duty solenoid valve 2 is provided among a pressure chamber, a negative pressure chamber and an atmospheric pressure chamber in the engine and is operated upon receipt of a control signal from the engine ECU 1. On the other hand, the negative pressure chamber of the engine receives and regulates a negative pressure from a vacuum pump 4, thereby operating the negative pressure actuator 3. The vacuum pump 4 circulates oil to carry out an operation. 5 denotes a turbocharger to be a so-called supercharging system of an internal combustion engine which controls the opening of a variable nozzle for causing the flow velocity of an exhaust gas to be variable which is provided in the turbocharger 5 by the operation of the negative pressure actuator 3. In the drawing, 6 denotes a pressure sensor which is provided with a hose 6a placed in the exhaust gas flow path of the turbocharger 5, and the detection signal of the pressure sensor 6 is introduced into the engine ECU 1 through a communication line 6b. 
Moreover, another example in the conventional art includes a variable nozzle turbocharger control apparatus of an internal combustion engine which has been disclosed in JP-A-2001-107738, and FIG. 9 shows a structure thereof.
Description will be given to the structure. 7 denotes a turbocharger comprising a center housing, a compressor housing and a turbine housing.
In the turbocharger 7, an air intake inlet port 7a for introducing air and a compressed air supply hole 7d for supplying compressed air by the turbocharger 7 to the engine 8 are provide. Further, an exhaust gas sucking port 7c and an exhaust gas outlet port 7b for discharging the exhaust gas are provided in the turbocharger 7.
In the compressor housing, the air intake inlet port 7a for introducing air to be supplied to the combustion chamber of an engine 8 is provided in a portion positioned on the opposite side of the center housing. The turbine housing is attached to the other end side of the center housing, and an exhaust gas is sprayed onto the turbine housing and is then fed to a catalyst through the exhaust gas outlet port 7b in the portion positioned on the opposite side of the center housing in the turbine housing. A variable nozzle (not disclosed) provided in the turbocharger 7 is disposed between the center housing and the turbine housing. 9 denotes a stepping motor. By the driving operation of the stepping motor 9, an operating piece 10 is operated to press ring plates provided in the variable nozzles in the same direction, thereby regulating the size of a clearance between the vanes of the mutual variable nozzles. Thus, the flow velocity of the exhaust gas sprayed onto a turbine wheel is regulated. 11 denotes an ECU (electronic control unit) of the engine which serves to input the detected outputs of various sensors provided in the engine, to identify the operation state of the engine based on the detected outputs and to control the driving operation of the stepping motor 9, thereby controlling the opening of the vane of each of the variable nozzles to regulate the flow velocity of the exhaust gas sprayed onto the turbine wheel. Consequently, the amount of air to be fed forcibly for combustion is also regulated.
In the drawing, 12 denotes a radiator which is connected to the engine 8. The cooling water of the engine 8 is circulated in the radiator 12 and is thus cooled. 13 denotes a heater connected to the engine 8 in which the cooling water is heated so that warm air is fed into the interior of the car.
According to the conventional art, the whole position of the variable nozzle is set to be the initial position of the variable nozzle at time of the generation of the abnormality of the variable nozzle turbocharger control apparatus of the internal combustion engine, cold starting, the operation of a heater or idling. Consequently, precision in the control of the position of each nozzle vane in the vicinity of a full-open position can be enhanced, and furthermore, a controllability can be improved in a high rotation and low load operation state.
Since the conventional art has the structure described above, there are the following problems.
More specifically, in the former case of the conventional art, a control signal is generated from the engine ECU 1 and operates the negative pressure actuator 3 through the duty solenoid valve 2, thereby controlling the opening of the variable nozzle coupled to a link mechanism including a lever and a rod in order to control the opening of the variable nozzle provided in the turbocharger 5. The microcomputer constituting the engine ECU 1 is to calculate an air intake pressure, that is, a boost pressure in the supply of air to be taken into the engine to the air intake path. A data map having an engine rotation signal set to be an X axis, a fuel injection amount set to be a Y axis and a target boost pressure set to be a Z axis is stored, and a water temperature signal, a rotation signal and a load signal which are input from the sensor of the engine are read and a target boost pressure suitable for a signal amount is calculated. Furthermore, an actual boost pressure is detected from the pressure sensor 6 to operate the engine ECU 1 in response to an output signal. Accordingly, there is a problem in that the duty solenoid valve 2 and the negative pressure actuator 3 are caused to generate a misarrangement in an operation by precision in the sensor, a temperature drift or the linear interpolation computing error of the data map and the opening of the variable nozzle cannot be controlled properly.
In particular, the position of the negative pressure actuator 3 is determined by a regulated negative pressure amount and the spring pressure of a return spring. There is a problem in that the control software of the engine ECU 1 for carrying out a control operation to have an optimum value, and furthermore, for executing a deciding operation when the negative pressure actuator 3 requires a positive pressure and a negative pressure and the opening of the variable nozzle is improper has a load hysteresis increased remarkably and cannot exhibit a resolution.
Moreover, the engine ECU 1 and the duty solenoid valve 2 are provided in an interior and an engine room, respectively. A control signal line led from the engine ECU 1 to the duty solenoid valve 2 and the negative pressure actuator 3 is long and congested, and a noise is apt to be generated. For this reason, a countermeasure is to be taken against a noise, for example, the control signal line is to be shielded. Furthermore, the specification of the design of the duty solenoid valve 2 is complicated.
In addition, the duty solenoid valve 2 is connected to the negative pressure chamber of the negative pressure actuator 3 through the hose 3a, the vacuum pump 4 to be rotated by the engine is connected to the duty solenoid valve 2, and the opening of the variable nozzle communicating with the atmosphere is constituted by mechanical devices, that is, the negative pressure actuator 3 through the hose 3a. Consequently, there is a problem in that the hose 3a, and furthermore, the vacuum pump 4 are required, resulting in an increase in the size and complexity of a whole system.
In the latter case of the conventional art, as described above, the variable nozzle to be operated by the operating piece 10 is provided in the path for the exhaust gas to be sprayed onto the turbine wheel. The variable nozzle is opened and closed by the ring plate. In the variable turbocharger control apparatus of the internal combustion engine for regulating the flow rate of the exhaust gas, consequently, the initial position of the variable nozzle is determined and the opening of the vane of the variable nozzle is controlled at time of the generation of the abnormality of the variable nozzle turbocharger control apparatus of the internal combustion engine, cold starting, the operation of the heater or the idling of the internal combustion engine. Moreover, the driving operation of the vane of the variable nozzle is carried out by the rotating operation of the stepping motor 9. Consequently, the latter case has almost the same problems as those of the former case in the conventional art.
Thus, in the second example of the conventional art, the opening degree of the vane is identified and determined uniformly based on the initial position of the variable nozzle. Any offset control cannot be performed even in a case that the opening of the vane is shifted from the target opening degree. Therefore, it is difficult to control the position of the nozzle vane suitably in real time.